Isoprene from ethylene using olefin disproportionation

ABSTRACT

A PROCESS OF PREPARING ISOPRENE FROM ETHYLENE WHEREIN ETHYLENE AND BUTADIENE ARE CODIMERIZED TO PRODUCE A BRANCHED ACYCLIC DIENE, THE BRANCHED ACYCLIC DIENE IS CONTACTED WITH AN OLEFIN DISPROPORTIONATION CATALYST IN THE PRESENCE OF ETHYLENE TO PRODUCE THE ISOPRENE. THE BUTADIENE CAN CONVENIENTLY BE PROVIDED BY THE OLEFIN DISPROPORTIONATION OF PROPYLENE TO PROVIDE ETHYLENE AND BUTENES, AND SUBSEQUENT DEHYDROGENATION OF THE BUTENES.

2 Sheets-Sheet 1 PROPYLENE ISOPRENE R. L. BANKS HEAVIES INVENTOR R. L. BANKS ATTORNEYS mZON 21o Dec. 28, 1971 ISOPRENE FROM ETHYLENE USING OLEFIN -DISPROPORTIONA'IION Filed Jan. 8, 1970 ETHYLENE\ BUTADIENEq United States Patent 3,631,118 ISOPRENE FROM ETHYLENE USING OLEFIN DISPROPORTIONATION Robert L. Banks, Bartlesville, Okla, assignor to Phillips Petroleum Company Filed Jan. 8, 1970, Ser. No. 1,434 Int. Cl. CtWc 3/62, 11/18 US. Cl. 260-680 R 7 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates to the preparation of isoprene from ethylene. In a further aspect, the invention relates to a process for the preparation of isoprene from ethylene and butadiene.

Description of the prior art The reaction of olefinic materials to produce other olefinic materials wherein the reaction can be visualized as the breaking of two existing double bonds between first and second carbon atoms, and between third and fourth carbon atoms, respectively, and the formation of two new existing bonds, such as between first and third carbon atoms and the second and fourth carbon atoms, respectively, and wherein the two existing double bonds can be on the same or different molecules, has been called the olefin reaction. The olefin reaction can also be described mechanistically by visualizing two unsaturated pairs of carbon atoms combining to form a 4-center (cyclobutane) intermediate which then dissociates by breaking either set of opposing bonds. Other terms have been utilized to describe the reactions of olefinic'rnaterials which are within the scope of the olefinic reaction as defined above. These include such terms as olefin disproportionation, olefin dismutation, transalkylidenation, and olefin metathesis. Throughout this specification and claims, the term olefin disproportionation is used as a matter of choice, and is deemed to be equivalent to the abovementioned terms, including the olefin reaction.

Included among the reactions which fall within the scope of the term olefin disproportionation, there is a reaction which employs ethylene as one of the reactants. That is, ethylene with its double bond, is one of the unsaturated pairs of carbon atoms which combines to form the 4-center (cyclobutane) intermediate with another unsaturated pair of carbon atoms on a diiferent molecule. For example, ethylene and pentene-Z in the presence of an olefin disproportionation catalyst react to form butene-l and propylene. Because of the fact that the larger molecule (pentene-2) has been broken to form the shorter molecules -(butene-1 and propylene), this type of olefin disproportionation reaction has been called ethylene cleavage. Another term which has been applied to this type of reaction is ethenolysis. When the ethylene cleavage reaction is carried out in the presence of an olefin disproportionation catalyst in combination with a double bond isomen'zation catalyst, high conversions of olefinic feed materials to relatively low molecular weight olefinic products are obtained. This type of olefin disproportionation reaction has been called exhaustive ethylene cleavage.

Numerous catalyst systems have been reported which effect the olefin disproportionation reaction, including the catalysts of US. 3,261,879, Banks (1966) and 3,365,513, Heckelsberg (1968).

The petrochemical industry today is seeking new ways to prepare isoprene from various petrochemical feedstocks. The art has developed ways of producing isoamylenes via olefin disproportionation chemistry. These isoamylenes are then subjected to dehydrogenation to produce isoprene. However, the art has heretofore not been able to develop a process of preparing isoprene utilizing ethylene as a feedstock.

OBJECTS OF THE INVENTION It is an object of this invention to produce isoprene utilizing ethylene and butadiene as the feedstock.

It is a further object of this invention to produce isoprene using ethylene alone as the feedstock.

Additionally, it is an object to provide a desirable degree of flexibility to a butadiene manufacturing facility such that a single plant can produce both butadiene and isoprene in ratios of one to the other which correspond to the market demand.

Other objects and advantages of the present invention will be apparent from a reading of the following disclosure and the appended claims.

SUMMARY OF THE INVENTION The process of preparing isoprene comprises codimerizing ethylene and butadiene to produce a methylpentadiene codimer and subjecting this branched codimer to a catalytic olefin disproportionation reaction in the presence of ethylene which exhaustively cleaves the branched codimers to isoprene. Propylene is a byproduct of this reaction.

Further in accordance with this invention, isoprene is prepared from ethylene alone by the process of disproportionating byproduct propylene to provide ethylene and butenes, and dehydrogenating the butenes to butadiene.

. Butadiene and feed ethylene are then fed to the codimerization unit to produce the methylpentadiene codimer mentioned above, the methylpentadiene codimer being passed to another olefin disproportionation unit wherein it is exhaustively cleaved in the presence of ethylene to isoprene. The ethylene cleavage of the codimer produces sufficient quantities of propylene to provide substantially all of the feed requirements for the propylene disproportionation step.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawing is a schematic flow diagram which illustrates the preparation of isoprene utilizing the olefin disproportionation and ethylene/butadiene codimerization steps.

FIG. 2 of the drawing is a schematic flow diagram which illustrates the embodiment of the invention wherein isoprene is prepared utilizing ethylene alone as the feedstock.

DETAILED DESCRIPTION OF THE INVENTION Some of the principal reactions which are believed to take place in the codimerization zone are:

011 011 +H2=0H0H:CH2 o1 1 :0110rncnaon=on 011 :01 1 orr =cncn=cin orn=onornon=cnorn The efiluent of the codimerization reaction is withdrawn via line 4 and passed to olefin disproportionation (DPN) zone 66. Unconverted ethylene from the codimerization reaction and unconverted butadiene are also subjected to the exhaustive ethylene cleavage reaction within zone 66. The olefin disproportionation of the efiluent, containing a large proportion of ethylene, produces a variety of olefinic products including substantial amounts of isoprene. For best results, the molar ratio of ethylene to other olefins in the cleavage zone is at least 2:1 and preferably at least 4: 1. The isoprene is the result of exhaustive ethylene cleavage of the branched polyenes such as the methylpentadiene codimer. The other principal product of this cleavage reaction is propylene. Within zone 66, substantial amounts ofthe other unbranched codimerization byproducts such as cyclohexene and the linear hexadienes are reconverted to butadiene.

Some of the principal reactions which are believed to take place in the exhaustive ethylene cleavage zone are:

Isom. 0H =0H0H(0H CH GH 011 011 0 (CH CH OH,

Cleav.

Cleav. CH=CHCH 0H=CHCH 011 :011

Cleav.

Cleav.

Reactions 7 and 8 illustrate the simultaneous double bond isomerization and ethylene cleavage of methyl-substituted dienes which take place to produce the desired isoprene product. Reactions 9, 10, and 11 illustrate the analogous manner in which other unbranched dienes are reconverted to butadiene for recycle. Unbranched trienes follow this same route. Reaction 12 illustrates the conversion of the cyclic olefin to the acyclic diene, which can then proceed to butadiene as in reactions 9, 10, and 11.

The efiluent from disproportionation zone 66 is passed via line 6 to separation zone 68. Therein, ethylene and butadiene are separated and recycled via lines 7 and 8, respectively, to line 3 and to codimerization zone 64. Byproduct propylene is removed from the system via line 9. Unconverted codimerization products are returned to olefin disproportionation zone 66 by way of line 11. Heavier materials are removed from the process via line 12. Isoprene is passed from the separation zone 68 via line 13 and recovered as the product of the process.

In a modification of the process as depicted in FIG. 1, some or all of the propylene which is recovered as a byproduct of the process can be recycled to the olefin disproportionation zone 66 and utilized as a portion of the cleaving olefin. In this embodiment, butenes become a significant byproduct of the reaction within the disproportionation zone 66 and are recovered from separation zone 68 in any suitable manner.

A preferred embodiment of the invention wherein isoprene is produced utilizing ethylene as the feedstock is depicted in FIG. 2. FIG. 2 presents a schematic flow diagram wherein ethylene in line 21 is fed via line 25 into a codimerization zone 76. In line 25, the ethylene is admixed with butadiene from line 34 which is prepared within butene dehydrogenation zone 73. The propylene disproportionation zone 71 receives make-up propylene from line 22 and recycle propylene from separation zones 72 and 78 via lines 23 and 24. Within disproportionation zone 71, the propylene is converted to ethylene and butenes according to:

ZCH CHCH e CH =CH CH CH=CHCH The efiluent from the propylene disproportionation zone 71 is passed via line 26 into separation zone 72. From within zone 72, unconverted propylene is recycled to disproportionation zone 71 via line 24. Ethylene is carried overhead in line 27 into line 21 to provide a portion of the feed to the codimerization zone 76. Butenes are recovered in line 28 and passed to dehydrogenation zone 73. Any heavier hydrocarbons present in the effluent from the disproportionation zone 71 are passed from the system via line 45.

Within dehydrogenation zone 73, the butenes are converted to butadiene. The efiluent from dehydrogenation zone 73 is carried by line 31 to separation zone 74. Therein, hydrogen and light materials are recovered via line 32 and passed from the system. Unconverted butenes are separated and recycled via line 29 to zone 73. Butadiene can be recovered as a valuable product of the process from separation zone 74 by way of line 33. Butadiene is also passed via line 34 into codimerization zone 76 wherein ethylene and butadiene are converted to codimers such as 3-methyl-1,4-pentadiene, 1,4-hexadiene, 1,3-hexadiene, cyclohexene, and butadiene oligomers as discussed above with respect to FIG. 1.

The entire efiluent, containing the olefinic products and a substantial molar excess of ethylene from codimerization zone 76, is passed via line 38 into disproportionation zone 77 wherein the eflluent is contacted with an olefin disproportionation-isomerization catalyst system. This reaction produces isoprene as a result of the ethylene cleavage of the methylpentadiene, while the exhaustive ethylene cleavage of the linear codimers, butadiene dimers, and other butadiene oligomers results in the regeneration of substantial amounts of butadiene. Another substantial product of the reaction within disproportionation zone 77 is propylene resulting from the ethylene cleavage reactions.

The efiluent from the ethylene cleavage zone 77 is passed via line 41 into separation zone 78. Within separation zone 78, isoprene is recovered via line 44 and compounds heavier than butadiene oligomers are removed from the system via line 42 as heavies. The unconverted codimerization products are returned to olefin disproportionation zone 77 via line 39. Butadiene is recovered and recycled to the codimerization zone 76 via line 37. Ethylene is recovered and recycled to codimerization zone 76 via line 36. Propylene is recovered from separation zone 78 and passed via line 23 to line 22 and to propylene disproportionation zone 71 for conversion to ethylene and butenes.

As will be shown in greater detail in the illustrative examples, the system as depicted in FIG. 2 provides an efiicient way of preparing isoprene from ethylene alone. The quantity of propylene produced in the system is sufiicient 6 Any suitable reaction techniques can be employed to effect the olefin disproportionation reaction, such as fixed bed operation, fluidized bed operation, liquid phase batch continuous operations, and the like. Conventional methto satisfy the feed requirements for the olefin disproporods can be utilized to separate the materials in the process tionation reactor 71. Therefore, only makeup propylene streams, including fractionation, crystallization, adsorpneed be introduced via line 22 to the system. In addition, and the like. Fractionation is generally preferred tion, the quantities of propylene, ethylene and butenes where possible.

produced are sufiicient that enough butadiene is prepared The catalyst which is used for the codimerization of in dehydrogenation zone 73 to produce some butadiene as 10 ethylene and butadiene to produce the methylpentadiene an additional product of this embodiment of the process. codimer may be any catalyst which suitably effects the The step requiring the dehydrogenation of butenes to codimerization of these two feed components to the parbutadiene can be carried out by any suitable catalytic ticular branched codimer. A particularly suitable cataprocess. For example, dehydrogenation processes employlyst is one which results from the admixture of ferric ing catalysts such as the well known iron-potassia-chromia chloride, triethylaluminum, and triphenylphosphine, catalysts, 01 a catalyst such as lithium-treated tin oxidewherein the P/Fe molar ratio is 1-2, the Al/Fe molar ratio tin phosphate catalysts can be used. is 3-5, and the ethylene pressure is about 500-150 lbs./

The olefin disproportionation steps of the invention are in. g. when the reaction is effected in the liquid phase at carried out using suitable catalysts. Any catalyst having a t ratur of 68 86 F, activity for olefin disproportionation reactions can be em- Th ethylene d b t di n hi h are employed as the p y These include solid (heterogeneous) and solution feed to the codimerization unit may be prepared by any (homogeneous) catalysts, combinations thereof suit method suitable in the art. A particularly suitable method able catalysts include those diSClOSfld in US. Pat. 3,261; for pre aring ethylene and butadiene from naphthalene is 879, Banks US 1 Heckelsberg (1 disclosed in US. 3,345,285, Hutto et a1. (1967). Although and HOWIIlaIl et and 1 25 feed materials can sometimes be processed in a crude Plieation Zlleeh, filed 1968, state, it is preferred that feed materials be suitably purified n w issued 1971- Eithel' prior to the reactions Within the steps of the invention. Solid Solution Olefin disproportionation catalysts can be The following illustrative example is presented in order used fer the P py disproportionation P Solid to explain the invention; however, the data included hereeatalysts are Prefen'ed the ethylene cleavage P 30 in should not be construed as limiting the scope of the portionation step. invention.

Some examples of preferred olefin disproportionation ILLUSTRATIVE AM 1 fid il a 13 2) iyO ifil O ah d t lil agii Ethylene and butadiene are converted into isoprene ac i f i gg 3 3 2 cording to the flow diagram as shown in FIG The codi- In that olefin disproportionation step of the process s i g? 64 fi i g i g f fi wherein the effluent from the codimerization reaction is y 5 ernc c on S y np any phosphme and 93 parts by Weight trlethylalumlnum. The exhaustively cleaved with ethylene, the olefin dlsproporo reaction conditions lnclude a temperature of 80 F., a tionation catalyst 1s utilized in COIljllIlCtlOIl with or assoressure of 1 000 Si and a Wei ht houfl S ace V6100 ciation with a suitable double bond isomerization catalyst 40 5y of 12 g y p such for example magnesium Oxide The presence of The eth lene cleavage unit 66 utilizes 40 parts by weight the double and lsomenzfanon. catalyst greatly gl fi of 8 weight percent tungsten oxide on silica catalyst ad the onverslon.to the deslled lsoprene and lene mixed with 240 parts by weight magnesium oxide. The particularly suitable combined catalyst for th1s step of tungsten oxide on silica/magnesia mixture is activated the process is silica-supported tungsten oxide combinawith air in an inert gas at 11000 R for 5 hours and tion with magnesium Oxide in the form of a mixed bed sequently treated with carbon monoxide at 1100" F. for in Which the Mgo is Present in amounts of Parts 15 minutes. Reaction conditions within the olefin disprog P P s z by Weightportionation unit 66 include a reaction temperature of Because of the wide variety of catalysts available for 725 F, a pressure of 500 i,g nd a space velocity use in the olefin disproportionation reaction, the temperaf 11, tures, pressures, fi fates, molar ratios 0 c talyst to feed Table I presents a material balance showing the commaterials, and other operating conditions will vary over position of the streams which are depicted within FIG. 1.

TABLE I Stream No.

Composition, wt.parts/hr. 1 2 4 6 7 s 9 11 12 13 Ethylene.. 92s 1,623 1,000 1,000 Propylene. 795 Butadlene- 317 80 683 Isoprene 410 Methyl pentadiene 360 36 Hexadiene 545 Methyl heptatriene 180 Oetatrlene 100 Others 40 Total 928 317 2,928 3,049 1,000 683 795 121 40 410 Table I shows that 928 wt. parts/hr. of ethylene and 317 wt. parts/hr. of butadiene are converted to 410 Wt.

parts/ hr. of isoprene. The process also provides 795 wt.

parts/ hr. of propylene.

ILLUSTRATIVE EXAMPLE II The process of the invention wherein ethylene is converted into isoprene using the codimerization of butadiene and ethylene in combination with olefin disproportiona- Reasonable variations and modifications of my invention steps is shown by the following material balance. In tion are possible without departing from the spirit and accordance with FIG. 2, the codimerization zone 76 is scope thereof. operated at the same conditions as codimerization zone I claim: 64 mentioned above in Illustrative Example I. However, 1. A process of preparing isoprene from ethylene which the catalyst comprises 54 parts of ferric chloride, 130 comprises the steps of (a) codimerizing ethylene and butaparts of triphenylphosphine, and 140 parts of triethyldiene to produce a stream comprising a methylpentadiene aluminum. Olefin disproportionation zone 77 is operated codimer, (b) olefin disproportionating said codimer in at the same conditions as olefin disproportionation zone the presence of ethylene to produce a stream comprising 66 mentioned above in discussing Illustrative Example I. isoprene.

However, Q catalxst composition P 60 P of 2. A process according to claim 1 wherein step (a) tungsten OXlde on 511195 and 360 Parts magnesla y Welghtalso produces unbranched olefinic addition products; and

The propoylene disproportionation zone 71 uses 100 step (b) also produces quantities of propylene.

parts by weight of a tungsten oxide on silica catalyst acti- 3. A process according to claim 2 further including as vated at 1000 to 1100 F. in flowing air for 5 hrs. The 15 s ep separating the isoprene-containing stream to p conditions for the conversion of propylene to ethylene Vide all ethylene recycle Stream, a butadiene recycle and butenes in zone 71 are a temperature of 750 F., a Stream, a P py Stream, 'isoprene Product Stream, pressure of 300 p.s.i.g., and a weight hourly space velocity and an unconverted codimerllatlon Product stream- Of 4. A process according to claim 3 further including step Dehydrogenation unit 73 uses 3600 parts by weight of (d) returning the ethylene recycle stream and the butaa dehydrogenation catalyst comprising iron, potassium, dlene recycle stre,am 9 f' (a), and Step (e) Tetummg the and chromia as described in Us 2 866 790 Fitz unconverted codimerization product stream to step (b). 5. A process according to claim 4 further including 2 i i i ggi, g g fi' igigz g z providing the butadiene for step (a) by the steps of (f) me u e a empera ure 0 P olefin disproportionation of the propylene produced by at the Inlet gaseous space veloclty of hydrostep (b), said olefin disproportionation provided a stream carbon of 400, and the ratio of volumes of steam to volcomprising ethylene and butenes and (g) dehydrogenat of hydrocarbon of 12/1- ing the butenes to provide said butadiene.

The composition of the streams as depicted in FIG. 2 A process according to claim 5 wherein ethylene 0f the drawing are Shown in Table produced in step (e) is utilized as at least a part of the Table II illustrates that 992 wt. parts/hr. ethylene can h l f ed to Step be converted to 615 Wt. parts/hr. 0f isoprene. The process 7, A process according to claim 1 wherein the ratio additionally can produce 75 wt. parts/hr. of butadiene. of ethylene to other olefins in step (b) is at least 2 to 1.

TABLE II Stream No.

Ethylene Propylene 1, 200 Butencs Octatriene Others Total 902 0 1,200 1,800 3,000 400 735 1,720 2,455 185 475 1,500 1,023 4,300 4,570 52 65 G1 References Cited UNITED STATES PATENTS 3,408,418 10/1968 Iwamoto et al 260-680 OTHER REFERENCES Heckelsberg et al.: Diene Disproportionation Reactions. In J. Catalysis, vol. 13, pp. 99-100, January 1969.

PAUL M. COUGHLAN, JR., Primary Examiner US. Cl. X.R. 260-680 B 

